Gradient Pore-Structured Polymeric Fibrous Aerogels for Effective Low-Frequency Noise Absorption

Traffic and industry noise have been considered the most disturbing pollutants that induce severe health hazards to humans. Porous materials are commonly used for sound-mitigating applications; however, realizing high elasticity and sound-absorption ability at low frequencies has remained a great challenge. Herein, we report a strategy to create gradient-structured ultralight weight and elastic polymer-based fibrous aerogels by layer-by-layer assembly of polymer micro- and nanofibers in different combinations, utilizing step-by-step directional freezing and freeze-drying methods. This approach allowed us to integrate poly(ethylene terephthalate) microfibers (MF) and polyvinylidene fluoride nanofibers (NF) in different combinations, and the combination with MF/(MF and NF blend) MNF/NF units shows the best noise reduction coefficient of 0.66. Compared to the individual aerogels of MF, MNF, and NF, the gradient-structured fibrous aerogels show a better sound-absorption ability at low frequencies. The gradient-structured fibrous aerogels exhibit ultralightweight, elasticity, and good mechanical properties. The successful fabrication of these fascinating structures may provide innovative prospects for the utilization of used plastics for the production of low-frequency noise absorbers.